Knife holder for cutting machines

Abstract

A knife holder for cutting machines, with a cutter head (1) for holding a knife (2) and a positioning device (3), wherein the positioning device (3) can be driven in a drive direction (4) between a standby position and a cutting position, and comprises a spring (5), with which the positioning device (3) is applied against the drive direction (4), wherein the spring (5) generates a reset force having a negative force characteristic curve in the drive direction (4).

Claims

1. A knife holder assembly for cutting machines, the knife holder assembly comprising: a cutter head (1) for holding a knife (2); and a positioning device (3), wherein the positioning device (3) comprises: a piston apparatus (7) configured to drive the knife a drive direction (4) between a standby position and a cutting position, and a spring (5), wherein the spring applies a reset force against the piston apparatus while the knife is in the cutting position, wherein the spring (5) generates the reset force having a negative force characteristic curve in the drive direction (4), such that the reset force generated by the spring acting transversely to a longitudinal axis of the spring and against the piston apparatus (7) diminishes with an increasing travel distance in the drive direction (4) from the standby position to the cutting position and wherein the longitudinal axis of the spring (5) is aligned at an angle (6) of 30 to 80 relative to the drive direction (4) when the knife is in the standby position.

2. The knife holder assembly according to claim 1, wherein the spring (5) is arranged and/or designed in such a way that the reset force having the negative force characteristic curve corresponds to the progression of a force characteristic curve generated by a drive of the positioning device (4) in the drive direction (4).

3. The knife holder assembly according to claim 1, wherein the reset force generated by the spring (5) also includes a force direction inclined to the drive direction (4).

4. The knife holder assembly according to claim 3, wherein the spring (5) counteracts a torque generated in the cutting position by pressing the knife (2) against a counter knife (13).

5. The knife holder assembly according to claim 1, wherein the spring (5) is a helical spring.

6. The knife holder assembly according to claim 1, wherein the piston apparatus (7) is pressurizable.

7. The knife holder assembly according to claim 6, wherein the spring (5) acts on the piston apparatus (7) on a side facing away from a pressurizable side.

8. The knife holder assembly according to claim 7, wherein the piston apparatus (7) comprises two membranes (8.1, 8.2), between which a pressurized fluid can be introduced.

9. The knife holder assembly according to claim 8, wherein the two membranes (8.1, 8.2) have different sized active surfaces.

10. The knife holder assembly according to claim 8, wherein the piston apparatus (7) has a multipart piston head (9.1, 9.2), and the membranes are fixed in place by the multipart piston head (9.1, 9.2).

11. The knife holder assembly according to claim 6, wherein the piston apparatus (7) has a piston rod designed as an axis (10), and the axis (10) is at least axially movably mounted by means of a bearing (11).

12. The knife holder assembly according to claim 1, wherein the knife holder assembly further comprises a lowering device (12) for the cutter head (1), wherein the lowering device is configured to move the cutter head (1) in a direction orthogonal to the drive direction (4).

Description

(1) The invention as well as the technical environment will be exemplarily explained below based upon the figures. Shown schematically on:

(2) FIG. 1: is a sectional view through a knife holder in a standby position,

(3) FIG. 2: is a sectional view through the knife holder in a cutting position,

(4) FIG. 3a: is the progression of the force exerted on the knife by a drive as a function of the adjustment path according to prior art,

(5) FIG. 3b: is the progression of the reset force exerted on the knife by the spring as a function of the adjustment path according to prior art,

(6) FIG. 3c: is the progression of the resulting force exerted on the knife as a function of the adjustment path according to prior art,

(7) FIG. 4a: is the progression of the force exerted on the knife by a drive as a function of the adjustment path according to the invention,

(8) FIG. 4b: is the progression of the reset force exerted on the knife by the spring as a function of the adjustment path according to the invention,

(9) FIG. 4c: is the progression of the resulting force exerted on the knife as a function of the adjustment path according to the invention.

(10) The knife holder also comprises a positioning device 3, with which the circular knife 2 can be set in a drive direction 4 that is orthogonal to the drive direction of the lowering device, for example on a lower knife 13 (e.g., a counter knife 13).

(11) The knife holder also comprises a positioning device 3, with which the circular knife 2 can be set in a drive direction 4 that is orthogonal to the drive direction of the lowering device, for example on a lower knife.

(12) The positioning device 3 comprises a positioning piston apparatus 7. The positioning piston apparatus 7 comprises a multipart positioning piston head with a first positioning piston head part 9.1, a second positioning piston head part 9.2 and a screw 9.3, which connects the positioning piston head with an axis 10. The axis 10 is mounted by means of a bearing 11 so that it can be displaced along a straight line in the drive direction 4. The positioning piston apparatus 7 also comprises two membranes 8.1 and 8.2. The first membrane 8.1 is clamped between the first positioning piston head part 9.1 and the second positioning piston head part 9.2, while the second membrane 8.2 is clamped between the second positioning piston head part 9.2 and the axis 10.

(13) It is also provided that compressed air can be introduced between the two membranes 8.1 and 8.2. Since the membranes 8.1 and 8.2 have different sized active surfaces, the positioning piston apparatus 7.1, and thus also the circular knife 2, is moved in the direction of the drive direction 4 by feeding in compressed air.

(14) The force exerted on the knife by feeding in compressed air between the membranes 8.1 and 8.2 diminishes as the travel distance from the standby position shown on FIG. 1 increases.

(15) In order to provide a reset force from the cutting position shown in FIG. 2 into the standby position shown in FIG. 1, a spring 5 designed as a helical spring is provided, the spring axis of which is inclined by an angle 6 relative to the drive direction 4.

(16) While moving the positioning device 3 from the standby position into the cutting position, the spring 5 acts on the positioning piston apparatus 7 with a force opposite the drive direction 4. Since this force acts transversely to the longitudinal axis of the spring 5, the reset force diminishes with an increasing travel distance. As a result, the total force acting on a lower knife 13 (e.g., a counter knife 13) remains constant, regardless of the position along the adjustment path.

(17) While pressing the circular knife 2 against a lower knife 13 (e.g., a counter knife), a torque is also introduced into the cutter head 1, which acts around an axis that is orthogonally aligned to the drawing plane. Because it is arranged inclined to the drive direction 4, the spring 5 can also counteract this torque, thereby diminishing the friction between the axis 10 and bearing 11.

(18) FIGS. 3a to 3c denote the force exerted on the knife by a component (FIGS. 3a and 3b) and by the entire system (FIG. 3c) as a function of the adjustment path for prior art, while the corresponding force progressions on FIGS. 4a to 4c are denoted for the present invention.

(19) FIGS. 3a and 4a show the force exerted on the knife 2 by the drive of the positioning device 3. As evident, this force diminishes with an increasing travel distance.

(20) FIGS. 3b and 4b show the reset force exerted by a spring. According to prior art (FIG. 3b), for example as known from DE 102 60 031 B3, the reset force provided by the spring increases with an increasing travel distance, while according to the invention, the reset force acting against the drive direction 4 diminishes with an increasing travel distance. Therefore, the spring 5 according to the invention yields a negative force characteristic curve of the kind shown on FIG. 4b.

(21) FIGS. 3c and 4c show the total force resulting from the positioning device and the spring. According to prior art (FIG. 3c), the resulting force diminishes with an increasing delivery path. As evident from FIG. 4c, a total force that remains constant over the adjustment path is provided according to the present invention owing to the negative characteristic curve of the spring 5.

REFERENCE LIST

(22) 1 Cutter head 2 Knife 3 Positioning device 4 Drive direction 5 Spring 6 Angle 7 Positioning piston apparatus 8.1 First membrane 8.2 Second membrane 9.1 First positioning piston head part 9.2 Second positioning piston head part 9.3 Screw 10 Axis 11 Bearing 12 Lowering device